Astronomy

Can I build a telescope with a lens from a CD-ROM as eyepiece?

Can I build a telescope with a lens from a CD-ROM as eyepiece?



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I saw some article on the web about making an eyepiece of a telescope with the lens from a CD-ROM. Will this really work? I have an objective lens of 100 cm focal length. What will be the magnification if I could make a refractive telescope? Can I see the planets and moon with that? Can anyone suggest the arrangement of the lenses?


Eyepieces are carefully designed. They try to achieve a sharp image with good contrast over a wide field of view. Even the simplest eyepieces of type Huygens consist of two lenses that match up. Good eyepieces can have 7 or more lenses.

In the end every eyepiece is a fancy magnifying glass, so your CD ROM lens will work. It will just not make for a good image. It'll be much worse than the 10/25mm Plössl eyepieces that so many sell for cheap or sometimes even give away. They sell them for cheap because even though they are much better than any single lens, they are still on the lower end of the quality spectrum.

Another problem is: the CD ROM lens has a tiny focal length which will result in very high magnification and a very dark image. A rule of thumb says: twice your mirror diameter in mm is about the useful upper limit for magnification. If you have an 8" reflector, that would be 200mm x 2 = 400x.

Nonetheless an interesting experiment. You can try to put a cardboard ring in front of your telescope to give it a longer focal ratio. It might help a little while costing a lot of light and resolution.

You can see 5 planets without any magnification. To see details, I'd say the fun starts at around 150-200x even though they appear as a disc at much lower magnification.


As to what the focal length of your eyepiece will be, you can refer to this paper, in particular Figure 1 from which I derived the following relation:

$f=0.73r$

where $f$ is the focal length of your lens, and $r$ its radius (this is a rough approximation, of course). So given the fact that a typical CD drive lens is about 5mm in radius, its focal length will be only a few millimeters.

Now, assuming the focal length of your telescope is 1000mm, the magnification will be a few hundred times. What you will be able to see with that depends on the width of your objective lens and how well you will have built your eyepiece, but you should probably be able to see the Moon with your custom eyepiece. As for the planets, it will be hard to get something good given how much you are magnifying-not impossible, but be aware that magnifying several hundred times requires a good weather, a good telescope and a good eyepiece.


Can I build a telescope with a lens from a CD-ROM as eyepiece? - Astronomy

The beauty of Chuck's method is that no lathe is required – only a table saw and a drill press. In a pinch, you could make the eyepieces with only a drill press by using a hand saw to cut and shape the wood housings. I already had a drill press and had been looking for an excuse to purchase a small table saw. Soon, an inexpensive Craftsman table saw found a place in my garage workshop.

I am a relatively inexperienced woodworker, so I began experimenting with scrap pine lumber to learn how to rip it into the octagonal shape suggested by Chuck in his article. It turned out to be relatively easy.

Chuck recommended using walnut for the eyepiece housings. After failing to find the recommended walnut stock locally, I found Woodcraft on the web. They sold me a small quantity of 2" × 2" walnut in 30" lengths.

To help you select lenses for making your own eyepieces, I have prepared two Eyepiece Focal Length Calculators . There are both online and downloadable versions of the calculators.

A trip to a local hobby store turned up styrene plastic for spacers and thin plywood for retaining rings. Careful bidding on eBay yielded an inexpensive set of Forstner drill bits for boring out the wood housings.

When the 2" × 2" walnut stock arrived, I used the table saw to rip it into an octagonal shape, measuring 1.625" between opposing faces. I measured the lenses, spacers, and retaining rings, and calculated the required length of each eyepiece housing. Then I cut off segments of the octagonal stock to the required lengths.

The most difficult part of this project is to accurately bore out the housing. You must bore three different diameters. The three borings must be concentric and centered in the housing, and each must be bored to the correct depth. If your woodworking experience and equipment are similar to mine, expect to make some mistakes.

I have prepared some construction illustrations showing the sequence of steps involved in boring out a housing and illustrating how the components fit together. Since your lenses will probably not have the same physical dimensions as mine, there is no point in my providing exact measurements you must determine them for yourself once you have all of your components in hand.

I then made the housing for the 19mm Erfle, and after one very silly measuring mistake, I created a near-perfect housing on the second try. The old rule of "measure twice, cut once" must have been created just for me.

I found it very helpful to make a simple jig for holding the eyepiece housings in place while drilling. Here are some photos of the jig.

Once I had bored housings, it was time to make them look pretty. Using a sanding drum in the drill press, I chamfered the corners of the housings, then used sandpaper to further soften the edges by hand. Each housing was finished with two coats of clear spray-on polyurethane, with a light sanding between coats. I used flat black paint to make a glare-reducing annulus around each eye hole, as suggested in Chucks' article.

And the Verdict Is .
The eyepieces perform very well! I tested them in my C5 5" SCT with a f/.63 focal reducer. The 19mm has a true field of 1.2° and is nice and sharp in the center two-thirds of the field, with performance falling off at the edges. The eye relief is generous, though not quite enough to let me see the whole field while wearing eyeglasses. I'll use this eyepiece a lot, because it neatly fills a gap in my range of available magnifications.

The 23mm has a true field of more than 1.4° and is similarly sharp until you reach the outer third of the field. Its eye relief is perfect for me while wearing my eyeglasses. It makes a nice star hopping eyepiece, though I won't be giving up my 30mm Celestron Ultima. The 23mm will be a fine eyepiece for public observing sessions.

I am delighted with these eyepieces. With nothing but these two eyepieces and a 2x Barlow, I could spend many happy nights under the stars. And you can't beat the feeling of accomplishment that comes from creating something useful with your own two hands.


UNISTELLAR EVSCOPE EQUINOX: FIRST IMPRESSIONS

The eVscope eQuinox isn’t identical to its predecessor, the eVscope. Though it looks the same at first glance, its tube is a dark grey rather than light grey and, of course, there’s no eyepiece. Whether or not you see that as a positive or a negative, it has consequences, largely by allowing the telescope to have a much longer battery life. Whereas the original telescope worked for 10 hours, the eVscope eQuinox works for 12 hours.

Perhaps more crucially it’s got a lot more storage space than the original eVscope, with a healthy 64GB versus 12GB. Why is not immediately clear since the resolution of the images it produces hasn’t changed, remaining at 1.27 megapixels. However, during our review a firmware update upped that to an impressive 4.8 megapixels thanks to some advances in its image-stacking algorithms. Backyard astrophotography is on!


Step 2: Making the Optical Tube of the Telescope

The first thing that you have to prepare is the optical tube of the telescope, to make that you will need 90 cm of the 60 mm weldable pipe and 20 cm of the 50 mm weldable pipe, with these pipes in hand you will have to paint the inside of these two pipes with matte black spray paint.

After painting the pipes, you should take the 50 mm pipe and at one end, place a layer of double-sided tape. And then place the 50 mm pipe inside the 60 mm pipe. See the images below.


Meade Infinity 209004 – Best Backyard Telescope Under $200

  • Type: achromatic refractor
  • Aperture: 80mm (3.2″)
  • Focal length: 400mm
  • Focal ratio: f/5
  • Mount: altazimuth
  • Eyepiece: MA 26mm, 9mm, 6.3mm, 1.25″
  • Weight: 11 lbs.

Other features: fully coated optics, red-dot viewfinder, 2x Barlow lens, Autostar® Suite Astronomer Edition Software

The Meade Infinity is supplied with an impressive accessory kit. There are three eyepieces 26 mm, 9 mm and 6.3 mm, a steel tripod with an Alt Azimuth mount and more. This makes it easy to set up your telescope and make adjustments as necessary to locate night sky objects. Despite all of these accessories, the Meade Infinity weighs just 11 pounds.

This makes it one of the best backyard telescopes under $200, but it also offers the flexibility to pack it up and take it on astronomy adventures away from home. This telescope is the ultimate grab and go kit. With its shorter focal length, this scope provides expansive views for bright deep sky objects and bright clusters.

The refractor optical design ensures sharp images that require no collimation. This is a fully accessorized, lightweight scope that is great for night or day, sky or land.

Why did it make our list?

  • Impressive kit that includes multiple eyepieces, tripod, and Autostar software.
  • Lightweight and easy to set up

What is not ideal about it?


Definition of lens and basics

A lens is an optical device that transmits a light beam by refracting it. The lens is most commonly made from glass, and/or some types of plastic and the material is ground and polished to the proper shape. The basic operating principle of a lens is that it focuses the light to create an image.

Most lenses are spherical lenses – the surfaces of the lens are a part of a sphere. The surfaces can be convex (protruding outwards), concave (depressed inwards) or planar (flat).

The lenses that focus the light beam into a focus spot are called positive or converging lens the lenses that scatter the light beam are called negative or diverging lenses. These types of lenses are the most common in telescopes, binoculars, monocular and other optical instruments, and the ones we’ll talk about some more.

What is aperture?

On the front part of the telescope, the diameter of the opening where the light enters is called the aperture and is most commonly measured in inches or mm. This is also an important measure when we talk about telescopes and other optical devices that are directly dependent on light.

The aperture of a telescope is usually the diameter of the lens or mirror to the edges that hold it in place. The aperture is given in linear measurements, and when speaking about the performance of a telescope, this is a very important measure to know.

What is focal length?

The point where the beam of light that passes through the lens is called a focus and the length between the center of the lens and the focus point is called focal point. This is the most important measure for the lens.

The focal length is measured in millimeters (mm) and it points to the power of magnification of the telescope. The longer the focal length of a telescope eyepiece is, the higher the magnification and narrower field of view and vice versa.

How is magnification power measured?

We have mentioned above that the focal length is in direct correlation to the magnification power of the telescope. The magnification power is the resulting number of dividing the focal length of the telescope and the focal length of the eyepiece.

So, by using telescope eyepieces with different focal lenses, you will get different degrees of magnification, thus getting the most of your telescope.

We should note here that there is a limit to the magnification power of the telescope, and this is called highest useful magnification. Going above the highest useful magnification means that the image will have low contrast and will be dim.

The common rule is that the highest useful magnification is 60 times the aperture of the telescope. For example, a telescope with 6-inch aperture will have a maximum power of 6 x 60 = 360x. Do not be fooled when someone will advertise a telescope with a ridiculously high power of magnification, and with very small aperture.

What are exit pupil and eye relief?

The exit pupil is the image of the object that is created by the eyepiece. The exit pupil size is the ratio between the aperture and the magnification of the telescope. The distance where you put your eye to see the full field of view in relation to the eyepiece is called the eye relief and is directly correlated to the exit pupil.

The increase of the power of the telescope lowers the exit pupil. Also, the human eye has a pupil that extends between 0.5mm and 7mm, so when you are looking for appropriate eyepieces for your telescope, the exit pupil size (in relation to the telescope) should be between 2mm and 6mm.

The eye relief is an important factor with the telescope eyepiece. The larger eye relief means that the optimal viewing distance is further from the eyepiece, facilitating the viewing. But too large eye relief makes it harder for the viewer to remain the correct viewing position.

The most common eye relief distances are between 2mm and 20mm. This length should accommodate for the human eyelashes and should not cause discomfort. People wearing eyeglasses should consider longer eye relief to accommodate for glasses.

What is a field of view?

Short definition – field of view is the extent of the observable world seen at a given moment. In terms of telescope eyepieces, the field of view is the area that can be seen when looking through the eyepiece.

This measurement varies depending on the magnification and design of the eyepieces. This is important to know when considering the size of the sky that will be visible when the eyepiece is used.

Barrel diameter of the eyepiece

The eyepiece on a telescope is interchangeable. This way they can accommodate increase and decrease of the magnification, and enable the viewer to have a more varied performance from the same telescope. For this to happen, the telescope eyepieces come in standardized barrel diameter.

The telescope eyepieces come in six standard barrel diameters, measured in inches:

  • 0.965 in – usually found in small telescopes like toy telescopes or shopping mall retail telescopes. These are usually made from plastic and even have plastic lenses. More expensive manufacturers usually do not produce this kind of standard barrel diameter eyepiece.
  • 1.25 in – the most common and popular eyepiece diameter. This eyepiece barrel diameter is limited to a 32mm focal length, because of the actual diameter of the barrel and the physical limit of its size. This telescope eyepiece barrel diameter is an excellent choice for the beginner size telescopes. It works with 30mm filters.
  • 2 in – the 2-inch eyepiece barrel diameter has a focal limit of 55mm, and gives more freedom in viewing, but can be more expensive, and heavier, even tipping the telescope. These work with 48mm filters.
  • 2.7 in – these eyepiece barrel diameters are more expensive and are made by fewer manufacturers. These have nice, wide field of view.
  • 3 in – the 3-inch barrel diameter allows for 120 degrees of field of view and very long focal lengths. These are, however, very expensive and heavy and only large telescopes can accept them.
  • 4 in – the largest barrel diameter eyepieces, these are used only in observatories. They are made by highly specialized manufacturers.

Building a telescope from a telephoto camera lens

About a year ago, I came across an article about how one could make a telescope using a telephoto lens and the eyepiece from a telescope. At the time, I didn't have a telescope and I was really chomping at the bit to get my hands on something, anything really.

So I set out to see if I could make this work, I know this is a terribly simple project compared to most of the endeavors of the ATM community, but it gave me a taste and I've already moved on to building a refractor (I'm not grinding my own lenses yet, but small steps!)

I thought I could detail the process for anyone who's browsing the ATM forums, looking for a starting place.

- Telephoto lens
- 1.25" telescope eye piece
- 1.25" drill bit
- Rear Cover cap for lens
- some additional material to help shore up the fitting(a small scrap piece of wood, plastic, etc)
- super glue

1.) The first step was to locate the center of the rear cover cap, fortunately for me, the exact center was marked with an injection point from the plastic cap being manufactured. (you probably can't see it in this picture, but it's right in the middle of the "k".)

2.) Using a 1.25" drill bit, I slowly and carefully drilled out the center of the lens cap.

3.) . till I had something that looked like this (The other cap is there for comparison)

4.) From there, I cut and drilled out two small pieces of masonite to help create a tube to hold the eyepiece. This helped keep the eyepiece correctly aligned with the lens as well as holding it firmly in place.

5.) I used a small amount of super glue to adhere the masonite and the lens cap together. While it dried, I inserted the eyepiece so it wouldn't shift out of alignment and dry permanently in place.

6.) Once the glue had set, it was just a matter of putting the cap back on and inserting the eyepiece.

It worked, better than I'd hoped, and I had a telescope, built out a second hand camera lens and an inexpensive plossl eyepiece. I could comfortably view the Orion Nebula as well as Saturn and one of it's moons.

Considering up until this point, I'd never seen either close up with my own eyes, it felt incredible!

I made a short video right after mounting the eyepiece for the first time. You'll have to excuse the shot through the scope, my camera doesn't quite come close enough to the eyepiece and it gives the impression you're looking through a key-hole.

#2 WillCarney

That works well. I cheated on mine. I bought a t-mount to 1.25" adapter. I just screw it into any of my t-mount camera lenses and I have a telescope. Of course it won't work on non t-mount lenses. But most of my telephoto's are t-mount so that's not a problem.


Can I build a telescope with a lens from a CD-ROM as eyepiece? - Astronomy

Build your own telescope with our AstroMedia cardboard kits that really work!

From the tiny, lipstick-sized Pocket Telescope to the Newton Telescope with dobsonian mount and 70mm mirror, all our telescopes are fully functional and building them is one of the best ways to learn how they work. You’ll also find some useful accessories at the bottom of this page.

A solar filter for the Newton Telescope. Use this filter to safely observe sun spots.

Also available as a set: see Special Offers

The Historic Galileo Telescope

This beautiful kit is based on the last remaining telescope that belonged to Galileo (the oldest telescope in the world): a leather-bound show piece with golden ornaments for Cosimo II de Medici, which now is on show in Florence.

With this historically accurate cardboard replica you can experience the great achievements of Galileo yourself. Although the performance of this historic telescope is not comparable to modern ones, it is fully functional and emphasises Galileo’s accomplishments.

High quality cardboard kit with four colour and gold print, complete with glass lenses for 12x magnification and wall/desktop mount.

Length of the telescope: 78 cm

Hint: mount the telescope on a normal tripod with our cheap Tripod Adapter (round), see below or on our Components page!

The Small Galileo Telescope

Two lenses connected by a cardboard tube: it’s that simple to build a telescope!

The prepunched kit contains an objective lens with 225 mm and an eyepiece lens with 35 mm focal length. This produces a magnification of 6.5.

The assembly is simple and takes only 20 minutes. An ideal project for scout groups and school classes. The picture is upright, therefore the telescope can be used by day or for astronomical observations (e.g. moon craters).

Length fully extended: 23 cm

This is a kit for a fully functional Newton reflecting telescope with Dobsonian mounting. The main BAADER glass mirror with SiO2 coating has a diameter of 70 mm and a focus length of 450 mm. Two eyepieces provide magnification factors of 16 and 30, enough for observation of moon craters and even the moons of Jupiter. If you want to mount the telescope on a standard photographic tripod, we can recommend our Flat Tripod Adapter 259.FSA further down on this page.

Scary buccaneer design with glittering gold print. Very simple assembly for old salts and land lubbers alike. Two lenses for 6.5 x magnification. Yarr!

Ideal for group work or children’s birthday parties.

Length fully extended: 23 cm

Build yourself a proper sailor’s telescope of the type that Nelson would have used. The five-section draw tube and two lenses provide you with 6x magnification. It even comes with a lockable container to protect it when you are on shore leave.


Celestron Travel Scope 70 Telescope Kit

The Celestron Travel Scope 70 Telescope Kit features all coated glass optical elements, so you experience nothing but the clearest, crispest images during both celestial and terrestrial observations. The erect image diagonal and smooth altazimuth mount ensures that you can correctly orientate your views and track objects with supreme ease and comfort. Furthermore, this exclusive package contains not only the standard 10mm and 20mm eyepieces and The Sky X – First Light Edition CD-ROM (featuring a 10,000 object database, colour images, custom sky chart printing and more), but also includes an additional 4mm eyepiece and 3x Barlow Lens to boost your viewing power.

Let's get this straight - The Celestron Travel Scope 70 Telescope Kit is not an astronomical telescope per se, yet you can do some astronomical observations with it with care. This is a scope that is intended to sling over your back, use as a spotting scope for bird watching, terrestrial scenic views and some night time astronomical use. The supplied lenses are also excellent and give a nice sharp view of the Orion Nebula, some of Jupiter's moons and Saturn, for example. So if it is a multi-use scope that you require then this is for you. And for the price you pay, even with the rather poor tripod that comes with it that makes night time astronomy a little tricky, you still get a great versatile scope that will cope with most daylight viewing well, and with some care also night time viewing too.

Box Contains

1 x Celestron Travelscope 70
1x Preassembled Aluminium Tripod
1 x Custom backpack
1 x 4mm Eyepiece
1 x 10mm Eyepiece
1 x 20mm Eyepiece
1 x 3x Barlow Lens
1 x Sky X - The First Light Edition


Can I build a telescope with a lens from a CD-ROM as eyepiece? - Astronomy

I personally buy from Ritz, Adorama and Amazon. I can't vouch for any other ads.

This fun accessory is no longer made.

It attaches to the back of any Nikon mount lens that has an aperture ring and makes it into a telescope. The newest G series lenses, which lack an aperture ring, won't work unless you bend the aperture pin with a hammer to keep the aperture open when mounted.

It contains an erecting prism and a 10mm focal length eyepiece.

The power of the telescope is therefore the focal length of your lens divided by 10. A 50mm lens becomes a 5x telescope, a 400mm lens is a 40x telescope, and a 70-210mm zoom is a 7-21 power zoom telescope.

If you are an idiot you can use it to make your 16mm fisheye into a potent 1.6x telescope, and your 8mm fisheye into an 0.8x reducer, and your exotic 10mm OP fisheye into a 1.0x scope. A better way to make a 1x scope is to use a toilet paper tube and no glass!

It has a dioptometric adjustment covering about -5 to +3 diopters.

It allows the full use of up to an f/3.5 lens aperture which provides up to a 2.8mm exit pupil. Faster lenses get no brighter 2.8mm is the maximum exit pupil.

The Lens Scope Converter works great. The limiting factor is the definition of the lens to which you are attaching it.

The image will be fantastic with ultra-sharp lenses like the 400/2.8 AF-I, and be poorer with lesser lenses.

Mediocre lenses will be on the fuzzy side.

It has enough magnification to allow you to see lens aberrations that you cannot see on film.

This is a fun and useful device, if you can find one. There are discount brands like Bower made today that are not as good, even though they have the same specifications.

I got a deal when I got mine used in 1995 for $80. As of September 2005 one just sold on eBay for $327 here.

I found the 500mm f/8 C reflex lens to be very well suited to this converter because the reflex lens is crappy for photography, but has great central definition.

Make sure to set the lens to its widest aperture, and not the minimum aperture to which most AF lenses are left set with the aperture ring stop. If you don't change the lens aperture you will get a very dark image. This converter has no pin to open the automatic diaphragm of the lens.

Since the exit pupil is limited to 2.8mm you can stop your lens down to f/3.5 to attempt to reduce flare.

Feel free to use teleconverters between the Lens Scope Converter and you lens for more magnification.

Remember that this converter doesn't use the entire image area, just a small area of the center of the lens' image.